A tufting machine produces carpet through the use of a needle bar assembly containing a plurality of needles. The needles stitch yarn for producing the carpet while one or more needle bars move in a side-to-side motion. At a first position (i.e., "home" position), the needle bar is disposed at a starting location within the carpet stitch pattern. At a second position, the needle bar may be displaced horizontally to the right while stitching the carpet. At a third position, the needle bar may again be displaced to the right. After a series of such steps and stitches of the carpet pattern, the needle bar is displaced horizontally in the opposing direction. After a number of steps have been completed, for example 22 steps, the needle bar will have returned to the home position in the carpet stitch pattern. The above process is repeated to produce tufted loop carpeting. In one common technique, the carpet produced by this process has a series of zig-zag edges due to the horizontal left and right displacement of the needle bar. This horizontal displacement helps alleviate some of the defects produced in the manufacture of the carpet, or creates a desired visual appearance.
During normal operation, a tufting machine operates by rotating a main drive shaft at about 450 to 1150 revolutions per minute. The main drive shaft is coupled either directly or indirectly to the needle bar(s) that stitches the carpet. A programmable logic controller ("PLC") and an inverter drive are commonly used to control the starting and stopping (i.e., drive motion) of the tufting machine. A repeating carpet pattern may be created by a shifting needle bar action produced by a mechanical shifter, hydraulic shifter or other linear displacement mechanism to produce the desired carpet pattern. An encoder detecting system may be employed to track the position of the needle bar assembly within the needle stroke. A count of the steps taken within each pattern can then be communicated by the encoder to a controller. Each time the needle bar completes a pattern cycle, the controller counting the steps is reset.
In the event of yarn breakage or other error condition, the operator of the tufting machine can engage a stop button, or another stop mechanism (i.e., end out detectors) can be engaged, to halt the machine. When the stop signal is received, the operation of the tufting machine typically ramps down to approximately sixty revolutions per minute. This speed is commonly referred to as the "jogging speed" of the machine. Due to the physical momentum introduced by the size of a tufting machine, it may take a series of individual steps for the machine to slow down to reach the jogging speed. For example, where a carpet pattern includes 22 steps and the operator hits the stop button at step 4, it may take 15 steps before the machine reaches the jogging speed. At the jogging speed, therefore, the machine will have progressed to step 19 in the carpet pattern. After reaching the jogging speed, the tufting machine is braked for needed repair or maintenance of the carpet.
When restarting the machine, a defect may be produced along a given line in the carpet because the tension and feeding of the carpet at that line may result in yarn being tighter or looser than before. To reduce the risk of such a defect, the prior art discloses a method of stopping the needle bar at a given height (i.e., relative position of the drive shaft) within the needle stroke. This technique only alleviates some of the risks of a defect. If the machine is stopped at a point which is far away from a preset stop position, defects may also arise even if the needle bar is stopped at the height taught by the prior art. The prior art thus lacks the advantage of stopping the tufting machine at or about a predetermined step in the stitch pattern such as, for example, the next desired stop position, with a minimum number of jog steps, while at the same time stopping the needle bar at a given height within the needle stroke.
It is therefore an object of the invention to stop a carpet tufting machine at a preset stop step in the carpet pattern.
It is also an object of the invention to stop the needle bar of a carpet tufting machine at the next predetermined stop position and at a certain orientation of mainshaft rotation.
It is a further object of the invention to employ a programmable logic controller and encoder to stop a tufting machine at the next home position.
It is yet another object of the invention to minimize the number of jog steps prior to halting the needle bar at the predetermined stop step.